Create authenticated POST endpoint for dynamic inventory app

[rjw57]

Part of #33

Create authenticated POST endpoint for birthscream.

The endpoint should require an appropriate Django create/write permission for the user.

The endpoint should be authenticated. This could be via basic auth.

When a JSON document is uploaded to the endpoint, a corresponding record in the database is created. The record contains the JSON document in a JSONB field and the creation time. When a new record is uploaded, all but the N most recent documents for a given host are deleted. N is configurable but defaults to 50.